Inductor coil



T. H. LONG lINDUCTOR COIL June 6, 1933.

Filed Nov. 25, 1950 lllll l -22-!!11222.55!!! -t l ENTOR TTORNEY lThomas H. L 077g.

Patented June 6, 1933 lUNITED STATES PATENT OFFICE THOMAS H. LONG, OFIRWIN, PENNSYLVANIA, ASSIGNOR T0 WESTINGHOUSE ELECTRIC MANUFACTURINGCOMPANY, A CORPORATION OF PENNSYLVANIA INDUCTOR COIL Application ledNovember 26, 1930. Serial No. 498,415.

My invention relates to inductive heating and particularly to energizingcoils for inductive heating devices.

An object of my invention is to provide a novel, simple and highlyeflicient energlzing coil for an inductive eating devlce.

Another object of my invention is to provide an energizing coil for aninductive heating device that includes only one turn adjacent to thematerial being heated, thereby greatlyreducing the possibility of adestructive short circuit in case the material belng heated is moltenmetal, and part of it escapes from the containing Crucible.

Another object of my invention is to p rovide anV energizing coil thatshall be effective to reduce the stirring action caused bytheelectromagnetic field, by reducing the radial component of the field.

In practicing my invention, I provide an energizing coil in which theconductor is constituted by a relatively thin solid sheet or sheets ofcurrent-conductin material, the

tot-al width being substantial y the same as the axial length of thecoil, wound in spiral form to constitute a plurality of layers or turns.A plurality of spaced turns are constituted by fluid-traversed portions,also traversed by the current, and a plurality of air spaces niay beinterspersed with the fluid-cooled layers.

In the single sheet of drawing:

Figure 1 is a view, partially in side elevation and partially invertical section, through an induction furnace including the coilembodying m invention.

Fig. 2 is an en arged fragmentary view, in vertical section through thecoil, taken on the line II-II of Fig. 1,

Fig. 3 is a schematic view in radial section throu h one-half of a coilembodying a modiflged form of my invention,

Fig. 4 is an extended view of the conductor shoiwn in section in Fig. 3of the drawing, an

Fig. 5 is a schematic view, in vertical section, of a modified form ofcoil embodying my invention. l

Referring more particularly to Fig. 1 of the drawing, I have thereillustrated a crucible 11 adapted to contain metal to be melted which isintended to be illustrative of any material which may be heated or heattreated by inductive action.

A coil 12, constituting more particularly my invention, includes aplurality of spiral layers 13 of a suitable conductor which ispreferably made in the shape of a solid sheet of highlyelectric-conducting material, such' as copper. The width of theconductor 13 is substantially equal to the axial length of the materialto be inductively heated or, in other words, the strip or sheet ofcopper constituting the conductor is as wide as the energizing coil islong, axially of the structure.

A strip 14, of a suitable electric-insulating material, is locatedbetween the adjacent layers of the electric-conducting material 13 andextends to within the innermost layer of the coil.

The innermost layer of the coil is constituted by a double-wallstructure ..16 which may be b'uilt up of two cooperating thinner sheets17 and 18 (see Fig. 2) which are soldered or brazed together at theiredges in order to provide a double-wall fluid-conducting structure, theparts 17 and 18 being separated by a plurality of thin metal strips 19,which are shown in broken lines in Fig. 4 of the drawing.

An inlet 21 and an outlet 22, each of tubular construction, are securedto the opposed corners of the double-wall structure in order to permitsuch structure to be traversed by a cooling fluid.

I have illustrated two additional fluidand-electric-conducting layers inFig. 1 of of the drawing, only one of these being shown in Fig 2 of thedrawing, in order that a substantially uniform and relativel .lowtemperature may be maintained within the energizing coil structure.

As an additional means for effecting a reduction in the temperature ofthe energizin coil, I may provide two air spaces 23 and 24, each ofthese extendin through substanti ally 360 peripherally ofg the coilstructure. I have elected not to show the details of a clamping or of asupporting structure for the coil, as .these details constitute noparticular part'of m present invention.

Referencemay 'had to the sectional view of Fig. 2, whereln I have shownthe overla- `ping connection of the current-and-flui traversed art ofthe conductor and of the substantie ly shown, are overlap distance andsuita solid conductor which, as

for a short peripheral l brazed or soldered tothat the fluid-traversedether, in order ouble-wall-structuremay be conn .m series electriccircuit with the' other rtlon of the coil and conductor. Instead o usinga single sheet of conducting material, the width of which issubstantially equal to the axial length of the coil, I may use acplurality of narrower pieces of thin con- Fig. 3 of the rawing, will beprovided to extend radially of the coil. This, of course,

is in addition to the desired number of fluidconducting la ers and inaddition to the axially exten ing air (gaps 23 and 24, as shown in Fig.1 of the rawing.

It is obvious that the innermost fluidcooled layer will be highlyeffective in renducing the amount of heat which can flow from thematerial being heated in the crucible 11 to the rest of the coilstructure, and, in order'to make this innermost layer as effective aspossible, I refer to have any cooling fluid traverse t e innermost layerfirst and thereafter the other cooling-fluidtraversed structures, sothat the coolest cooling luid will be available at that part of the coilstructure subjected to the highest temperature.

The other layers of double-wall structure, traversed not only by anelectric current but also by a cooling fluid, will be effective toensure a low and substantially uniform temperature in a relativelycompact coil structure.

Referring to Fig. 5, I there illustra-te a modified form of coilembodying my invention. 31 indicates a mass of material to be heated,shown schematically only and supported by a base 32 of some suitablerefractory material. A coil 33 located beneath the base or support 32embodies al plurality of turns of a thin-metal-sheet conductor 34, woundin helical form, the adjacent turns being insulated from each other bysuitable means (not shown) in the usual manner. Water-cooled turns maybe em loyed in this form of coil, as were hereinbe ore described inconnection with Figs. 1 and 2.

A coil embodying my invention may have variousratios of the axial lengthof coil to the inner diameter thereof and I have found that my improveddesign of coil is very useful in energizing coils for the inductivetransfer of energy in which the axial length of the coil is equal to atleast one third of the internal diameter of the coil.

An important element entering into the design of induction coils theconductor of which is to be traversed by a' relatively heavy current isthe effect of leakage flux thereon. One leakage flux is that whichtraverses the space between the material being heated and the innereriphery of the coil, and a second leakage ux 1s that which is notinterlinked with all of the turns or layers of the energizing coil. Thisleakage flux is, of course, that flux which is located 1n, ortransverses the space occupied by the coil itself and flows in asubstantially axial direction.

In order to reduce the eddy-current losses in the conductor, it isdeslrable that the thickness of the conductor be made relatively smalland that the plane surface of the metal-sheet conductor extendsubstantially in thedirection of the leakage flux. The method ofdetermining the optimum thickness of such conductor is well known in theart and is substantially the same method as is used to determine theoptimum thickness of the conductors in large rotating machines. Havin inmind this consideration and also the di erent sizes of coils, both 'asto axial length and internal diameter, I prefer to ma e the ratio of thethickness of the conductor to its width less than one to twenty, or,stated in another way, the width of the sheet conductor is many timesits thickness. I find that this results in relatively low losses in theconductor, an important consideration when the material being heatedreaches relatively high temperature values, as, for instance whenmelting high-temperature alloys or heating metal ingots to rollingtemperature.

A coil of this kind will have a smaller radial component ofelectromagnetic field, in comparison with the axial component of thisfield, thus making it possible to utilize an electric screen of thegeneral kind disclosed and claimed in a copending application, SerialNumber 433,291, filed March 5, 1930 by myself and J. V. Breishy andassigned to Westinghouse Electric & Manufacturing Company, except thatthe shield need not be subdivided to reduce the eddycurrent losstherein.

One filed of application in which my improved coil may advantageously beutilized is in the welding of pipe blanks. In this kind of work, anenergizing coil is located either outside of a pipe blank to be weldedor on the inside thereof and is traversed by A `welding heat,

an alternating current of a suitable frequency to induce alternatingcurrent in the ipe blank of such intensity as to raise the a ting oroverlapping edges of the seam to a pressure or pinch rolls beingprovided to effect the weld, such devices being old in the pipe-Weldingart and hence not illustrated here in detail.

As thepcoil is. stationary. and the pipe blank is moved relativelythereto, some difficulty has been experienced heretofore in inductivepipe welding machines embodying energizing coils of the type including aplurality ofturns per layer located in side-byside relation. When theleading end of a pipe blank is located intermediate the ends d of thecoil, axially thereof, that part of the coil 'not covered by the pipeblank acts as a reactor, thereby reducing the value of the currenttraversing the coil and making it substantial-ly impossibleto effect aperfect Weld untilall of the coil length is covered. The result of thisis that a at each end Imust be cut ofl, thereby vreducing the output ofperfect pipe, or, in other Words, reducing the length of perfect pipewhich can be obtained from a given length of pipe blank.

If a coil of the kind hereinbefore described is used as the energizingcoil in a pipe-Welding machine, the effect is quite different, in fact,the coil operates as one having an inlinitely large number of turnsconnected in parallel-circuit with each other.

Assumingthat the leading end of a pipe blank is at about one-fourth ofthe axial length of the coil, that is, about one-fourth of the axiallength of the coil is covered by the pipe blank, the part of the coilthus covered Will be provided with a closed-cin cuit secondary ofrelatively low ohmic resistance While the uncovered part of the coilwill ordinarily tend to act as a reactor. In the present type of coil,however, the two paths, i. e., the low-reactance part and thehigh-reactance part of the coil are in parallel and, hence, the effectof the part of the coil momentarily unprovided with a secondary circuit,is almost negligible. A multi-layer singleturnper-layer coil of thiskind may, therefore, be utilized to advantage in Work such as pipewelding, the comments made Iabove applying both to ,the type of devicewherein the pipe blank surrounds or covers the coil and that in whichthe coil surrounds the pipe blank.

Various modifications may be made in the device embodying my inventionWithout departing from the spirit and scope thereof, and I desire,therefore, that only such limitations shall be placed thereon as areimposed by the prior art or are set forth in the appended clalms.

claim as my invention:

l. In an electric induction heater, a plu-v part of the pipe ing heated,said including a plurality ofradially-spacedindividual turns of adouble-Wall electric-conducting structure, and means for conducting acooling fluid to and from said individual turns. l

3. In anelectric induction heater, a plurallayer energizing coil yhavinga single turn per layer of a relatively thin solid-sheet conuctor andincluding. a pluralit of individual layers of a relatively thinouble-wall lluid-and-electric-conducting structure, one of said.last-named layers constituting the innermost layer of said coil.

4. In an electric heater for inductively heating material,a'plural-layer coil in inductive-energy-transferring relation tomaterial to be heated, said coil having a single 'turn per layer of arelativel sheet conductor, one layer of a lilid-andfelectric-conductingstructure located at that surthin solidface of the coil adjacent to thematerial bel coil including also a plurality of individual layers of afluidand-electric-conducting structure spaced throughout the thicknessof the coil,l all of said layers being velectricall connected in seriescircuit relation to eac other. l

5. In an electric induction-heater operatively associated with materialto be heated by inductive transfer of energy, an energizing coil havinga plurality of layers of va relatively thin solid-sheet conductor andone layer of a. fluid-and-electric-conducting element located at thatsurface of the coil adjacent to the material to be heated.

6. In an electric inductionheater, a plural-layerenergizing coil ininductive energy-transferring relation to material to be heated, saidcoil including a plurality of layers of arelatively thincurrent-conducting material, and at least one layer of acurrent-and-fluid-conducting structure Within the coil for cooling thesame.l

7. In an inductive heating device, a single turn per layer plural-layerenergizing coil embodying a conductor whose width throughout the lengthof the conductor is substantially equal to the axial length of the coil.

8. A device as set forth in claim 6 in which the Width of the relativelythin current-conducting material throughout the length thereof issubstantially equal to the axial length of the coil.

9. A- device as' set forth in claim 1 in which the Width oftherelatively thin metal sheet and of the cooling-fluid-conducting metalmember is substantially equal to the axial length of the energizingcoil.

10. A device as set forth in claim 6 in which t-he layer ofcurrent-and-luid-conducting structure is in series circuit relation tothe other layers.

11. In an electric induction heater, a plural-layer energizing coil ininductive energy-transferring relation to material to be 10 heated, saidcoil including a plurality of layers of a current-conducting sheet whosewidth throughout the length of the sheet is substantially7 equal to theaxial length of the coil to effect a predetermined current distributionaxially of the current-conducting sheet in accordance Withthe axiallocation of the material relatively thereto.

12. In an electric induction heater, a plural-layer energizing coil ininductive energytransferring relation to material to be heated, saidcoil including a pluralityr of layers of a current-conducting sheetwhose width throughout the length of the sheet is substantially equal tothe axial length of the 25 coil to automatically effect a greatercurrent density therein in that part thereof in axial juxtaposition withthe material being heated.

In testimony whereof, I have hereunto 3D subscribed my name this 21stday of November, 1930.

THOMAS H. LONG.

